By the way, what's your opinion about IQ you get with the V1 and the combo.
Is it far from the DSLR standard ?

Personally I am happy with the V1 IQ. In a way it is better than the d300s, especially when it comes to high ISO noise, I feel that the noise is lower and more pleasant. As a TC I think it is a very attractive solution since what are the alternatives? Optical TCs normally degrade the image, introduces CA and resolution loss, as well as light loss. The normal light loss for a 2x TC is 2 stops, with the V1 you will have no loss at all in terms of light but in terms of DOF.

Your 70-200/2.8 is in terms of light:

189-540/2.8 on the V1
105-300/2.8 on the DX

If you add the TC2 then the lens will behave like a 210-600/5.6 on the DX, so you gain 60mm but lose two stops of light.

Your 70-200/2.8 is in terms of light:

189-540/7.6 on the V1
105-300/4.2 on the DX

If add the TC2 then the lens is 210-600/8.4 on the DX (DOF wise), so you gain some 60mm but lose DOF. The loss of DOF with that focal length is not an issue but the loss of light is.

I would go for the V1 solution because the way I see it is that it offers some more potential, especially if you are not intending to use the highest quality TC available.

Please, don’t misunderstand my post. I don’t have the 70-200, so I have no experience with it. My experience on the V1 as TC is with the 70-300GVR and I am happy with the results, especially compared with what I could get using TC. I have never used the highest possible TC quality, but the ones I used had introduced some softness and CA, so I am generally against using optical TC.

Here are a few samples taken with the V1 and the 70-300 at 300mm. You may say that they are not great but I think they are good enough considering the focal length and the light.